On that build, you’ll see a lock with a cross through it when there’s a form element on the page but no HTTPS. This will happen even if you have HTTPS enabled but the form itself isn’t delivered over the secure protocol.

If it’s rolled out to all versions of Firefox, the change will have wide-reaching implications for a number of sites, since many include forms for things like newsletter signups but don’t bother encrypting those in transit as it’s not exactly sensitive information.

It’s good progress for browser builders to enforce stricter rules around HTTPS, given that it’s still frequently misused or forgotten. Google also added a feature to Chrome that will push developers to use HTTPS this week.